Acronym for "be back never", a derivative of brb. Used when one no longer has the desire to continue chatting, and wants to ditch the conversation.
Usually typed as brb, with the intent of bbn.
:Hey, he's so annoying, i'm gonna pull a bbn.
: sure =\
: yea, and then, bla bla bla...
: Hey man, brb.
*never comes back*